The kinetics of solid nucleation in zirconium

The framework of classical nucleation theory coupled with statistical analysis was used to evaluate nucleation data from zirconium undercooling experiments. Bulk samples of high purity zirconium were processed in a containerless, high vacuum environment using electrostatic levitation at Space Systems/Loral in order to obtain sets of nucleation temperature data. The relationships between undercooling and initial material purity have been investigated. The nucleation rate equation parameters, preexponential factor and work of cluster formation, were determined using a statistical analysis technique. The mean undercooling values ranged from 326 to 348 K for material purities between 99.8 and 99.995%, respectively. The range of values for the preexponential factors, 10(32)-10(43), and the activation energies, 64-88 kT, for the classical nucleation rate equation also scaled with the purity levels. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All lights reserved.